Chlorides, molten

It was an adaptation of the Castner cell to sodium chloride for fused caustic electrolysis. A mixture of sodium chloride and other chlorides, molten at 620°C, was electroly2ed ia rectangular or oval cells heated only by the current. Several cells have been patented for the electrolysis of fused salt ia cells with molten lead cathodes (65). However, it is difficult to separate the lead from the sodium (see Electrochemical processing). 

Heated zirconium is readily chlorinated by ammonium chloride, molten stannous chloride, zinc chloride, and chlorinated hydrocarbons and the common chlorinating agents. It is slowly attacked by molten magnesium chloride in the absence of free magnesium, which is always present in the KroU process. 

Electrolysis. Electrowinning of zirconium has long been considered as an alternative to the KroU process, and at one time zirconium was produced electrolyticaHy in a prototype production cell (70). Electrolysis of an aH-chloride molten-salt system is inefficient because of the stabiUty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the stabiUty of in solution, decreasing the concentration of lower valence zirconium ions, and results in much higher current efficiencies. The chloride—electrolyte systems and electrolysis approaches are reviewed in References 71 and 72. The recovery of zirconium metal by electrolysis of aqueous solutions in not thermodynamically feasible, although efforts in this direction persist. 

Examples of reactions that have been carried out in these antimony(III) ionic liquids include the cyclizations of l,2-bis-(9-anthryl)-ethane (Scheme 5.1-12) and 1,2-bis-(l-naphthyl)-ethane (Scheme 5.1-13). A more detailed review of antimony(III) chloride molten salt chemistry has been published by Pagni [4]. 

Catodic reduction and anodic oxidation of tantalum and niobium can also be performed in other molten media. Descriptions of processes that take place in chloride molten systems can be found in the literature [569 - 571]. 

Apart from the fluoride, mercuric halides react explosively with potassium like all analogues of the other metals already mentioned. With mercurous salts, the reaction seems less violent since with mercurous chloride, molten potassium causes the mixture to incandesce without ever combusting. It is likely that other metals react too an extreme violent reaction was mentioned between indium and mercuric bromide. 

Fig. 3.10 Mott-Schottky plot for n-type and p-type semiconductor of GaAs in AlCls/n-butylpyridinium chloride molten-salt electrolyte [79],...

Wilkes, J. S., Frye, J. S., and Reynolds, G. F., W1 and C NMR-studies of aluminum-chloride dialkylimidazolium chloride molten salts, Inorg. Chem., 22, 3870,1983. 

Ackermann, B. L., Tsarbopoulos, A. and Allison, J., Fast atom bombardment mass-spectrometric studies of the aluminum chloride N-butylpyridinium chloride molten-salt. Anal. Chem., 57,1766,1985. 

An electrolysis reaction in which the oxidation reaction is not the reverse of the reduction reaction is the electrolysis of molten sodium chloride. Molten sodium chloride (NaCl), with calcium chloride (CaCy added to decrease the melting point, is electrolyzed in a Downs cell, in which the sodium and chlorine products are separated so that sodium chloride does not reform. The following reactions occur ... 

A common type of ionic lattice is that of a crystalline salt. One such ionic lattice encountered in everyday life is sodium chloride. Molten sodium chloride is a typical liquid electrolyte and displays the characteristics of many liquid electrolytes. ... 

The Electrolysis of Molten Sodium Chloride. Molten sodium chloride (the salt melts at 801° C) conducts an electric current, as do other molten salts. During the process of conducting the current a chemical reaction occurs—the salt is decomposed. If two electrodes (carbon rods) are dipped into a crucible containing molten sodium chloride and an electric potential (from a battery or generator) is applied, metallic sodium is produced at the negative electrode—the cathode—and chlorine gas at the positive electrode—the anode. Such electrical decomposition of a substance is called electrolysis. 

Figure 7. Mott-Schottky plots for n- and p-type GaAs electrodes in an AlCfi-n-butylpyridinium chloride molten-salt electrolyte. (Reproduced with permission from Ref. [32].)...

Figure 23 contains an example of the APE for the n-GaAs-AlCl3/ -butylpyridinium chloride molten salt electrolyte interface [253]. The bottom curve is... 

Xu XH, Hussey CL (1992) The electrochemistry of gold at glassy caibon in the basic aluminum chloride-l-methyl-3-ethylimidazolium chloride molten salt. J Electrochem Soc 139 3103-3106... 

Chen PY, Sun IW (2001) Electrodeposition of cobalt and zinc-cobalt alloys from a Lewis acidic zinc chloride-l-ethyl-3-methylimidazolium chloride molten salt. Electrochim Acta 46 1169-1174... 

Buchanan and coworkers studied the behavior of various aromatic compounds in antimony(iii) chloride molten salts [84]. These salts can both act as a mild Lewis acid and allow redox reactions to take place. The Lewis acidity of the melt can be tuned by controlling the concentration of [SbClz] in the melts. Basic melts are formed by adding a few mol% of a chloride donor such as KCl, whereas acidic melts are formed by adding chloride acceptors such as AICI3 (Scheme 5.2-35). 

In an electrolytic cell, electric current drives the chemical reaction. The chemical reaction involved in an electrolytic cell is nonspontaneous. Electric current is used to drive the reaction. This process is called electrolysis and hence the name, electrolytic cell. The reaction involves the transfer of electrons and thus it is a redox reaction. For further understanding of the functioning of an electrolytic cell, we will look at an example of an electrolytic cell involving the electrolysis of molten sodium chloride. Molten sodium chloride is a good conductor of electricity. The melting point of NaCl is around 800° C. 

Fig. 23 Experimental data embodying APE for the n-GaAs-AICls/n-butylpyridi-nium chloride molten-salt electrolyte interface. Refer to the text for details. (Reproduced with permission from Ref 167.)...

This is of course not the case when working with room temperature ionic liquid systems. Electrochemical and spectroscopic studies of cobalt, copper, and nickel, have been carried out in the AlClj-butylpyridinium chloride molten salt system. The direct current and pulsed current electrodeposition of Ni-Al alloys has also been shown in acidic AlCls-butylpyridinium chloride ionic liquids. This particular alloy has also been shown to be successful in AlCl3-[C2-mim]Cl ashave Co-Al andCu-Al. Electrochemical techniques can also be used to calculate the diffusion coefficients of metal ions. Table 21.2.6 shows the calculated diffusion coefficients and stokes-Einstein products of cobalt(II), copper(I), nickel(II) and zinc(II) in the 40-60 mol% [Cj-mimlCl-AlClj ionic liquid. 

Pickup, R, and R.A. Osteryoung. 1985. Charging and discharging rate studies of polypyrrole films in AICI3 l-Methyl-(3-ethyl)-imidazolium chloride molten salts and in CH3CN. JElectroanal Chem 195 271. 

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